Method of removing air from goods in preparation for autoclave sterilization



Nov. 5, 1968 B. A. BJQRK 3,409,389

METHOD OF'REMOVING AIR FROM GOODS IN PREPARATION FOR AU'IOCLAVE STEHILIZATION Filed Sept. 16, 1964 Min. Min

PRIOR ART 0 R Fig.2

PRIOR ART Fi if' INVENTOR. Berg? A. Bjar'k KZWWM ATTORNEYS United States Patent METHOD OF REMOVING AIR FROM GOODS Y IN'PREPARATION'FOR AUTOCLAVE STERILIZATION a Bengt A. Bjork, Getinge, Sweden, assignor to- Getinge Mekaniska Verkstads Aktiebolag, Getinge, Sweden, 2! Swedish joint-stock company Filed Sept. 16, 1964, Ser. N0. 396,929 r h Claims priority,'application Sweden, Sept. 16, 1963, 10,130/63; Oct. 4,1963, 10,875/63 3 Claims ..(Cl.'2156) V 1 ABSTRACT on THE prscLosunn H Removing air from.good s. .in a space during.; a pretreatment period to prepare such goods ,for subsequent sterilization by steam in the space, such pretreatment period, including a first step in'.which fluid initiallyvis evacuated from the space to reduce the pressure thereinto a first vacuum, a second step in which steam is introduced into the space to increase the pressure thereinto a. partial vacuum which is at a lower vacuum than the first vacuum and below atmospheric pressure, a third step in which fluidthereafter is evacuated from the-space to reduce the pressure therein toward the first vacuum, .and a fourth step in which steam is subsequently introduced into the space to increase the pressure therein toward theipartial vacuum whieh is at a lower vacuum than the first vacuum and below atmospheric pressure, and evacuating fiuid from the space, during the first portion of each of the second and fourth steps while steam is being introduced into the space to promote removal of air from the goods -to prepare such goods for subsequent sterilization by steam in thespace.

treatment period to prepare such articles or -materialfor subsequent sterilization in the autoclave.

perature conditions as a function of time when the towels undergoing sterilization have been prepared for such It is common practiceto subject the articles or material to be sterilized to vacuum prior to the sterilization period in order toextract air from the articles or material. Moreover, ,itis well known to subject the articles of material to alternating positive pressure periods and vacuum periods during a pretreatment'period to prepare such articles or materialifor subsequent sterilization by steam.

A considerable inconvenienceof these heretofore known methods is that; due to unsatisfactory extraction of air from'the articles orrnaterial during the pretreatment period, it is necessary during subsequent sterilization of the articles or material to use high temperatures during a long sterilization period in order to secure sterilization of the interior of the articlesor material, such as, for example, a bundle of towels or similar articles.

The? object of the.invention isto' providea simple and F reliable method'to remove air from articles'or material during a pretreatment period to prepare such articles or material for subsequent sterilization 'by'steain,

The pretreatment period is started by first connecting the interior of the autoclave to a vacuum pump. When the pressure in the autoclave has been reduced to a first vacuum, steam is introduced into the autoclave to increase the pressure therein to a partial vacuum which is at a lower vacuum than the first vacuum and below atmospheric pressure. The foregoing treatment is repeated one or more times prior to the main or primary sterilization period. It is to be noted that the entire pretreatment of the articles or material is carried out below atmospheric pressure between a first vacuum and a lower partial vacuum which, to an essential extent, has promoted removal 3,409,389 ljatented Nov. 5, 1968 "ice of-.air--from articlesand material to prepare them for subsequent sterilization and has contributed to improved sterilization results under ditficult conditions, such as, for example,- the sterilization of tightly-l compressed articles ormaterial; p

According to a preferredrembodiment of the invention, which will become apparent from the following description, further advantages are obtained during .a pretreatment; period whereby, after-the first :vacuum has .been produced in an-autoclave by the vacuum pump,v steam is introduced into the autoclave to increase the pressure .therein;to a partial vacuum-(which is at a-lower .vacuu'm than-the firstvacuum and below' atmospheric pressure and thevacuum'pumpis connected to the autoclave'duringthe first'portion of the pressure build-up in theautocla'veythe vacuum pump being renderedinoperable when the pressure built-up in,theautoclave is intermediateand about midwaylbetween the first vacuum and-the partial vacuum produced in the autoclave at the conclusion of the period steam is admitted to the autoclave to build up the pressure therein. When the pressure increase in the autoclave is at the halfway mark between the first vacuum and the final partial vacuum which is lower than the first vacuum and below atmospheric pressure, the connection of the vacuum pump to the autoclave is closed or throttled whereby the steam will function to build up the pressure in the autoclave to the aforementioned finalpartial vacuum, afterwhich the connection to the vacuum pump is completely opened again when the pressure in the autoclave is built up to the aforementioned final partial vacuum which is below atmospheric pressure.

'This invention is explained hereinafter by referring to the accompanying drawing showing temperature conditions as a function of time in the interior of a bundle of towels compressed by a lead weight when the towels are being sterilized after first being prepared for such sterilization by different methods for removing air from the towels during a preliminary pretreatment period.

In the drawing, FIG. 1 diagrammatically shows .tem-

sterilization according to a conventional pretreatment method known in the prior art which includes a pretreatment period at 96% vacuum;

'FIG. 2 diagrammatically shows temperature conditions as a function of time when the towels undergoing sterilization have been prepared for such sterilization according to a conventional pretreatment known in the prior art which includes three vacuum periods and between these periods positive pressure periods at 0.9

(kilopond)/cm. that is, a pressure which exceeds atmospheric pressure by 0.9 kg./cm. ,or 1.9 atmospheres;

FIG. 3 diagrammatically shows temperature conditions as a function of time when the towels undergoing sterilization have been prepared for such sterilization according to a pretreatment method embodying my invention which includes three 80% vacuum periods and between these periods of vacuum having pressure build-up periods in whichthe pressure in the autoclave increases from a first vacuum to a partial vacuum which is at a lower vacuum than the first vacuum and below atmospheric pressure;

FIG. 4 diagrammatically shows temperature conditions as a function of time when the towels undergoing sterilization have been prepared for such sterilization according to a pretreatment method embodying my invention which includes the same pulsations given in the preceding example and further includes connecting the vacuum pump to the autoclave during the first portions of the pressure build-up periods and is disconnected from the autoclave when the pressures in the autoclave during the pressure build-up periods have increased about one-half of the'entire pressure increase in the autoclave from'the first vacuum to the partial vacuum which is lower than the first vacuum and below' atmospheric pressure; and FIG. sh'ows'the temperature conditions in the autoclave measured at the different measuring points when the articles are removed from the autoclave. i Each of the figures comprises three curves corresponding, in order from left to right, to a measuring point located in the center of the bundle of goods, a measuring point located between the preceding point and the top of the bundlev and a measuring point located above the bundle. From FIGURE 1 it will be evident that the temperature conditions as' a function of time according to this figure, which are encountered during sterilization, givesrise toconsid erable differences between the temperature in the interior of the bundle and the temperature at its surface. The time period, measured from the time I at which the surface of the bundle of autoclave temperature has reached the sterilization temperature of 138 C., to the time II necessary for the temperature in the interior of the bundle to rise to the sterilization temperature takes about 8 minutes. This indicates that the prior art pretreatment method for removing air from the towels to prepare them for subsequent sterilization, which includes a pretreatment period at 96% vacuum, is not satisfactory. In the sterilization methods employed according to FIGURE 2 and FIGURE 3, the corresponding time periods from time I to time II takes about 3 and 1 /2 minutes, respectively. This indicates that the pretreatment methods employed for removing air from the towels before sterilization in accordance with FIGURES 2 and 3, which pretreatment methods are given above in the explanation of FIGURES 2 and 3, are better than the pretreatment method employed to give the sterilization data shown in FIGURE 1 but still not completely satisfactory.

From FIGURE 4 it will be evident that the temperature in the interior of the bundle becomes heated to a temperature equal to the temperature at the surface of the bundle before the surface or autoclave becomes heated to the sterilization temperature. In FIGURE 4, therefore, the sterilization data shows that air has been removed effectively from the towels during the pretreatment period to prepare them for subsequent sterilization by steam in the autoclave. As pointed out above, this is due to the fact that during the pretreatment period the connection to the vacuum pump remains open when the first vacuum has been produced in the autoclave and steam is being introduced into the autoclave to build up the pressure therein, and subsequently the vacuum pump connection to the autoclave is closed when the pressure in the autoclave reaches the halfway mark between the first vacuum and the partial vacuum at the end of the pressure build-up period. Stated another way, fluid is evacuated from the space or autoclave during the first part of the pressure build-up in the space after the first vacuum has been produced in the space and while steam is being introduced into the space to increase the pressure therein to a partial vacuum which is lower than the first vacuum and below atmospheric pressure.

A very important advantage of the invention consists in being able to remove air effectively from material dur- 4 ing a pretreatment period to prepare such material 'for subsequent sterilization. This reduces the period of time during which the material to be sterilized is subjected to sterilization temperature without any likelihood of the 5 interior of the bundle of material not being sterilized due to the rate at which the temperature in the interior of the bundle of material lags behind the temperature at the surface of the bundle.

-W hatis claimed is:

1. A method of removing'air from goods in a space during, a pretreatment period to prepare such goods for subsequent sterilization by steam in the space, such method comprising thesteps of (a) initially evacuating fluid from the space to reduce the pressure therein to a first vacuum,

(b) subsequently introducing steam into the space to increase the pressure therein to a partial vacuum which is at a lower vacuum than the first vacuum and below atmospheric pressure,

(c') thereafter evacuating fluid from the space to reduce the pressure therein toward the first vacuum,

(d) subsequently introducing steam into the space to increase the pressure therein toward the partial vacuum which is at a lower vacuum than the first vacuum and below atmospheric pressure, and

/ (e) evacuating fluid from the space during the first portion of each of steps (b) and (d) while steam is being introduced into the space to promote removal of air from the goods to prepare such goods for subsequent sterilization by steam in the space.

2. The improvement set forth in claim 1 which comprises evacuating fiuid from the space during the first portion of each of steps (b) and (d) while steam is being introduced into the space and thereafter throttling the evacuation of fiuid'from the space in each of steps (b) and (d) for the steam introduced therein to function and increase the pressure in the space toward the partial vacuum which is at a lower vacuum than the first vacuum and below atmospheric pressure.

3. The improvement set forth in claim 1 which comprises evacuating fluid from the space during the first portionof each of steps (b) and (d) while steam is being introduced into the space and terminating the evacuation of fluid from the space in each of steps (b) and ((1) when the pressure in the space is intermediate the first vacuum and the partial vacuum which is at a lower vacuum than the first vacuum and below atmospheric pressure.

References Cited UNITED STATES PATENTS 2,132,095 10/1938 Broughton 34-15 1,778,079 10/1930 Kristensson 34-15 FOREIGN PATENTS 542,544 1/ 1942 Great Britain.

OTHER REFERENCES Howieet al., Sterilization by Steam Under Increased Pressure," Feb. 28, 1959, from the Lancet, pp. 425-427.

JAMES H. TAYMAN, JR., Primary Examiner. 

